Structure and Thermal <i>E</i>–<i>Z</i> Isomerization of Substituted 4-Phenylimino-5-pyrazolones and Hexafluoroacetone Anils

Hofmann, Hans‐Jörg; Asano, Tsutomu; Cimiraglia, Renzo; Bonaccorsi, Rosanna

doi:10.1246/bcsj.66.130

Cited by 10 publications

(2 citation statements)

References 16 publications

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“…For ground-state isomerizations with much larger barriers, polarization effects are usually less significant unless polar substituents are present and a reaction proceeds in a polar solvent; lowering of the energy barrier is especially important when the electronic push−pull mechanism is promoted by a pair of substituents, one of which is an electron donor and the other is an electron acceptor. This mechanism is efficient for compounds with NN double bond bridges; compounds such as 4-(dimethylamino)-4‘-nitroazobenzene (DNAB) and 4-(dimethylamino)-2‘-methoxy-4‘-nitroazobenzene (DMNAB) (see Table ) provide a typical example. 495b,,, However, the polar effect seems to be absent in the case of CN bridges where the reactive motion changes from an internal rotation to inversion at the nitrogen center.…”

Section: E Static Effects In Isomerization Reactionsmentioning

confidence: 99%

Activation and Reaction Volumes in Solution. 3

et al. 1998

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Section: E Static Effects In Isomerization Reactionsmentioning

confidence: 99%

Activation and Reaction Volumes in Solution. 3

et al. 1998

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“…Marullo and Wagener determined the free activation energies of the azomethines derived from aceton and aniline and benzylamine, respectively, to 21 kcal/mol and > 23 kcal/mol by measurement of the coalescence temperature 16c. Hofmann et al calculated on the STO‐3G level of theory values of 23−30 kcal/mol for the linear inversion transition state of three different anil types 16d…”

Section: Resultsmentioning

confidence: 99%

Metal 4‐Alkylidene‐4H‐pyridin‐1‐ides and 2H‐Imidazol‐4‐ones from Novel HighlyN‐(Pyridin‐4‐yl)methyl‐Substituted Azomethines

et al. 2004

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Novel azomethines 3 synthesized from 4‐(aminomethyl)pyridine (1) and various ketones 2 exhibit a higher acidity of the Cα‐protons compared with other 4‐alkylpyridines like 4‐benzylpyridine or 4‐(tosylmethyl)pyridine. Therefore, they can easily be metalated to give a variety of specific anions 3(−), which deserve interest for further synthetic applications. Important properties of compounds 3 and their lithiated derivatives 4 (lithium 4H‐pyridin‐1‐ides, synthesized by deprotonation of the α‐CH2 group in 3) can be controlled by the carbonyl reactant 2. These carbanions 3(−) are remarkable intermediates regarding their NMR properties. Comparing the NMR spectra of the lithium 4H‐pyridin‐1‐ides 4 with their parent azomethines 3 reveal very distinct changes in the chemical shifts from which important structural and electronic properties of the carbanions can be deduced. The observation of E/Z isomers in the case of 3c and their mutual conversion at higher temperature inspire DFT calculations on the B3LYP/6‐311++G(d,p) level of theory to get insight into the energetic demand of such isomerization processes. Moreover, calculations on the same level of theory were carried out on the model azomethine anion 5 and different monomeric lithium coordination isomers 6a−d. Experimentally, two selected examples will exemplify the reactivity of 4H‐pyridin‐1‐ide anions towards heterocumulenes. The 2‐(pyridin‐4‐yl)acetate 7 obtained from the reaction of 4e with carbon dioxide appears to be a CO2 storage molecule as it easily releases CO2 under protolysis conditions comparable with the vitamin B6 reaction mode. Interesting five‐membered heterocycles were isolated after reaction of 4 with isocyanates followed by hydrolysis and oxidation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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Enantioselective Generation of Adjacent Stereocenters in a Copper‐Catalyzed Three‐Component Coupling of Imines, Allenes, and Diboranes

et al. 2016

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Ah ighly enantio-and diastereoselective coppercatalyzedt hree-component coupling affords the first general synthesis of homoallylic amines bearing adjacent stereocenters from achiral starting materials.The method utilizes acommercially available NHC ligand and copper source,o perates at ambient temperature,c ouples readily available simple imines, allenes,a nd diboranes,a nd yields high-value homoallylic amines that exhibit versatile amino,a lkenyl, and boryl units.Enantiomerically enriched homoallylic amines are keystone building blocks,c rucial to the production of many important compounds,s uch as pharmaceuticals,n atural products,c atalysts,and ligands.[1] Tr aditionally,they are synthesized by the treatment of imines with allyl metal reagents or metalloids under reagent or substrate control, which provides homoallylic amines with magnificent stereoselectivity (Scheme 1A).[2] However,general methods for the enantioselective allylation of imines that forge adjacent stereocenters from achiral building blocks are rare,a nd typically use exotic imines. [3,4] This is likely due to the difficulty in forming isomerically defined allyl nucleophiles [5] and the low reactivity [6] and possible E/Z geometries of the imine coupling partner, [7] all of which affect the regio-and stereoselectivity during the subsequent coupling event.To keep apace with the demands of modern synthetic chemistry,m ulticomponent reactions must address challenging couplings in which numerous stereocenters are installed selectively: [8] If complex chiral products could be assembled from several readily available achiral components in ao nepot process,then diverse collections of high-value compounds could be quickly constructed by simple variation of the material inputs.I nr ecent times,e nantioselective multicomponent couplings with allenes have provided efficient methods for the synthesis of highly functionalized homoallyl stereocenters.[9] Fore xample,t he coupling of allenes and diboranes [10] with aldehydes or ketones [11] and allylic electrophiles [12] has been explored. [13][14][15][16] However,application to the synthesis of chiral non-racemic homoallylic amines has been surprisingly scarce, [17,18] given their importance,a nd this is likely due to the poor reactivity of imines. [6, 7] Morkens seminal report is the only example of an enantioselective multicomponent reaction coupling allenes,imines,and B 2 pin 2 (Scheme 1B).[19] Thep alladium-catalyzed process utilizes aT ADDOL phosphoramidite ligand, and initial asymmetric diboration [13c] of the allene component furnishes allylic boronic esters that are subsequently coupled with imines. Ther esultant highly enantiomerically enriched linear homoallylic amines were then oxidized and acylatedt of orm isolable b-amino ketones.H owever,i faprocess could be developed that employs alow-cost metal and acommercially available ligand, as well as utilizing aconvergent assembly of readily available achiral starting materials to generate homoallylic amines bearing adjacent stereocenter...

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Structure and Thermal E–Z Isomerization of Substituted 4-Phenylimino-5-pyrazolones and Hexafluoroacetone Anils

Cited by 10 publications

References 16 publications

Activation and Reaction Volumes in Solution. 3

Activation and Reaction Volumes in Solution. 3

Metal 4‐Alkylidene‐4H‐pyridin‐1‐ides and 2H‐Imidazol‐4‐ones from Novel HighlyN‐(Pyridin‐4‐yl)methyl‐Substituted Azomethines

Enantioselective Generation of Adjacent Stereocenters in a Copper‐Catalyzed Three‐Component Coupling of Imines, Allenes, and Diboranes

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